The present disclosure relates generally to the field of receiving and transmitting signals and more specifically to a diplexer and diplex method for steering wireless receive signals and signals for wireless transmission.
Receive-while-transmit operations for a frequency agile communication system (e.g., wireless communication system such as a radio frequency (RF) system) conventionally include significant system performance compromises in size, receiver sensitivity, transmitter power-efficiency, and frequency hopping speed. Conventional diplexers for full-duplex operation impose significant performance penalties, such as inefficient use of power, occupying large volume, and/or limiting bandwidth.
Historically, simplex operation has more frequently been employed instead of duplex operation. System costs associated with conventional diplexers/duplexers have been very high. High-speed data system proliferation in recent years may have changed the cost equation and greater emphasis can be placed on full-duplex capability. Looking forward, full-duplex capability may become standard for many more RF systems.
A diplexer may be used for separating a receive signal from a transmit signal and conventionally has a large volume or size when the transmit power is significant. A smaller diplexer conventionally has greater losses in both the transmit and receive paths due to a low quality factor (Q factor) of circuit elements. Low Q circuits have higher power dissipation relative to the operating frequency than in the larger diplexer and thus requiring the transmitter to produce more power. Frequency agility conventionally requires switching the diplexer frequencies of operation, introducing significant additional losses in both transmit and receive paths. High-speed frequency agility greatly compounds these issues.
One issue of conventional receive-while-transmit operations is the need to isolate the receiver input from the transmitted signal. The receiver input must provide sufficient filtering to reduce the strong transmit signal to a sufficiently low level to prevent overload of subsequent amplifiers. This isolation filtering is one function of a conventional diplexer.
Another issue of conventional receive-while-transmit operations is the need for noise from the transmitter to be reduced to near thermal background levels at the receiver or low noise amplifier (LNA) input. In most cases, due to antenna voltage standing wave ratio (VSWR) concerns, this requires that the power amplifier (PA) output be filtered to near background thermal noise levels because any isolating device between the PA and the receiver (e.g., a circulator) may fail to provide isolation when the undesired signal comes back directly from the antenna. Even modest VSWR levels, which cause little concern for the transmitter, may reflect noise and spurious signals within the receive band and degrade receiver performance. Conventional solutions to this problem have been to use separate receive and transmit antennas or to install very large diplexer filters to eliminate any noise present at the output of the transmitter/PA from being injected into the receiver front-end.
What is needed is a system and method having full-duplex capability while having low-loss transmission and low-noise receive operations What is also needed is a diplexer and diplex method having improved transmit and receive performance while reducing circuit size and cost. What is further needed is a diplex system and method for isolating the receiver input from the transmitted signal while reducing circuit size and cost. What is needed further still is a diplex system and method for reducing noise from the transmitter to near thermal background levels at the receiver or amplifier while reducing circuit size and cost.